This disclosure relates to the purification of proteins by precipitation. Ethanol precipitation is a potential alternative technology to chromatography for the purification of monoclonal antibodies (mAbs) from cell culture supernatants. This technology, first established by Cohn and co-workers (Cohn et al. 1946) for the production of plasma-derived intravenous immunoglobulin, is based on the variation of pH, conductivity, ethanol concentration, protein concentration and temperature. These new methods provide many advantages including, for example, antibody preparations suitable for formulation into pharmaceutical products as well as significant time and cost benefits.